Fuels from different sources may be mixed together to obscure the origin of one or more of the fuels. Fuels from different sources may be, for example, differentially priced fuels, such as taxed fuel and subsidized fuel or tax-free fuel, or different grades or types of fuel, such as kerosene, diesel fuel, low-octane gasoline, high-octane gasoline, and the like. In certain cases, higher priced fuel is mixed with lower priced fuel (e.g., lower grade fuel) or adulterants such as solvents. Fuel may be differentially priced for a variety of reasons. In some countries, liquid fuel, such as diesel fuel, kerosene, and liquefied petroleum gas, is subsidized or sold below market rates to provide more widespread access to resources. Fuel may also be subsidized to protect certain industry sectors, such as public transportation.
In some cases, subsidized fuel is purchased and then re-sold, sometimes illegally, at a higher price. For example, subsidized fuel may be purchased and then mixed with other fuel to disguise the origin of the subsidized fuel. In certain cases, markers placed in subsidized fuel for authentication are at least partially removed to disguise the origin of the fuel.